Citation:
N. Putnam, C. Marianno, N. Whitman, and S. Meijer “Special Nuclear Material Mass Estimates from Singles Rate”, Symposium on Radiation Measurements and Applications (SORMA), 21-24 July 2025, Berkeley, California.
Abstract:
Radioisotope Identification Devices (RIIDs) are useful detection devices for assaying systems with special nuclear material (SNM). These systems output American National Standards Institute (ANSI) standard n42 files containing the RIID gamma and neutron count rate. While neutron multiplicity detectors may provide higher fidelity neutron measurements than RIIDs, there are situations in which such a system is unavailable. An empirically informed algorithm for the RIID data could provide an improved capability for this application area. The objective of this research was to create an algorithm that will serve as a tool to provide a mass estimate of SNM using RIID neutron count rate data. To meet this objective, neutron count rate measurements of a 252-Cf source were taken at varying distances and moderation thicknesses with an ORTEC Detective X, FLIR IDentifinder 2, and ORTEC RADEAGLET-R. The purpose of these measurements was to establish a known absolute neutron efficiency for each RIID. An algorithm was created to estimate the mass of the unknown SNM utilizing the singles rate equation and the experimentally measured absolute neutron efficiency curves. Results show that this method can produce mass estimates ranging from approximately 1% to 10% difference from true mass in the Detective X and RADEAGLET, and 3% to 30% in the IDentifinder. This demonstrates the algorithm’s utility in calculating mass estimates, as well as the dependence on the type of RIID. This algorithm provides further capability to quickly and effectively predict mass of SNM utilizing relatively low neutron efficiency RIIDs.